In automatic transmissions, oil is circulated by a pump and used as a medium through which power is transmitted from an engine to driven components, such as vehicle wheels. Internal combustion engines use lubricating oil to provide a film of oil between opposing surfaces of components which have relative motion. In both cases, the oil entrains particulates which can damage the surfaces of the components. In both cases, it is necessary to remove the particulates in order to prolong the life of the transmission or engine. This is generally accomplished by a filter media which is porous in order to let liquid pass through but traps particulates on a "dirty side" of the filter media. One way to increase the useful life of a filter is to increase the dirt holding capacity of the filter by reducing the amount of dirt which must be trapped by the filter media.
One arrangement for a filter element which includes a filter media is to provide a panel having an opening therethrough in which the filter media is mounted. The panel is mounted in an oil pan between the bottom of the oil pan and the transmission case when the oil being filtered is transmission oil, or between an engine block and lubricating oil pan when the oil being filtered is lubricating oil. A primary interest is filtering transmission oil. In currently known arrangements, substantially all particulate matter is removed by the filter media itself, thus loading the filter media with all of the particulates removed from the oil. This, of course, limits the holding capacity of the entire filter to the amount of particulate matter which can be retained by the filter media itself.